Inorganometallic chemistry, atransition metal formyl complex is a metal complex containing one (usually) or moreformyl (CHO) ligand. A subset oftransition metal acyl complexes, formyl complexes can be viewed as metalla-aldehydes. A representative example is (CO)₅ReCHO. The formyl is viewed as an X (pseudohalide) ligand. Metal formyls are proposed as intermediates in the hydrogenation ofcarbon monoxide, as occurs in theFischer-Tropsch process.^[2]

The MCHO group is planar. A C=Odouble bond is indicated byX-ray crystallography. A second resonance structure has a M=C double bond, with negative charge on oxygen.

Metal formyl complexes are often prepared by the reaction of metal carbonyls with hydride reagents:^[3]

[Re(CO)₆]⁺ + H⁻ → (CO)₅ReCHO

The CO ligand is the electrophile and the hydride (provided typically from aborohydride) is the nucleophile.

Some metal formyls are produced by reaction of metal carbonyl anions with reagents that donate the equivalent of a formyl cation, such a mixed formate anhydrides.^[4]

Metal formyls participate in many reactions, many of which are motivated by interest in Fischer-Tropsch chemistry. O-alkylation gives carbenoid complexes. The formyl ligand also functions as a base, allowing the formation of M-CH=O-M' linkages.^[5] Decarbonylation leads to de-insertion of the carbonyl, yielding hydride complexes.^[2]

• Organometallic chemistry
• Transition metal compounds
• Coordination complexes